ABSTRACT
Carcinoid tumors are slow-growing malignancies with distinct biological and clinical characteristics. Because these tumors derive from neuroendocrine cell compartments, their frequency of occurrence correlates with the site-density of neuroendocrine cells. As such, over 60% of carcinoid tumors arise along the largest human endocrine organ, the intestine. Another common location is the bronchopulmonary system (25%), reflecting the high density of Kulchitsky cells in the respiratory epithelium. Other carcinoid tumors, however, occur infrequently and in obscure sites; their biological and clinical characteristics may not be as apparent.
